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A diesel fuel injector has been modified to allow rotation around its axis, driven by an electric motor. This enables sweeping injections in a DI Diesel combustion system. It has earlier been shown that sweeping injection enhances the air entrainment into the spray. This is one reason for the reduced smoke level by counter-swirl rotation of the injector. The injected amount of fuel is small and this enables exploration of spray / wall interaction and the effects of reverse-squish. Flame visualization shows that normal, non-sweeping injection tends to build up fuel pockets where the sprays hit the piston bowl wall. This fuel burns quite slowly since it only to a limited extent benefits from the mixing effects of the reverse-squish flow. Increasing the air swirl ratio from 1.65 to 2.47 does not reduce the impact onto the piston bowl wall much. The decrease in smoke level with increasing swirl was attributed to enhanced mixing of the fuel that had accumulated under the piston bowl rim.

HCCI-combustion with direct injection of gasoline using a standard GDI-injector is investigated in this work. The test engine is a 6-cylinder heavy-duty diesel engine with one cylinder operating in HCCI-mode. Exhaust gases from one of the diesel cylinders serve as simulated EGR. Electric heaters are used to raise the inlet temperature when no EGR is applied. The piston bowl is modified to match the hollow-cone spray better than the original re-entrant piston. Spray imaging outside the engine shows the characteristics of the fuel spray. Injection timing sweeps show that a homogeneous charge is created when the injection is performed in the middle of the intake stroke for a moderate fuel/air-equivalence ratio of 0.29. This leads to low emissions of NOx and Smoke. Using a homogeneous mixture when the fuel/air-equivalence ratio is reduced to 0.20 leads to low combustion efficiency with associated high levels of CO and HC emissions.

The injector in a DI diesel engine has been modified to allow rotation. The injector speed was varied within ± 4,000 rpm in the current study over 13 testpoints. Air swirl levels tested are 1.5 and 2.8. Rotating the injector adds a free parameter to the combustion system and enables lowest possible smoke emission from each given loadpoint. Smoke reduction up to 74% has been encountered. The mean reduction over all 10 testpoints with a swirl ratio of 1.5 is 55%. Increasing the air-swirl level decreases the smoke level with static injector. The further smoke reduction with counter-swirl rotation is significant albeit not as large as for the lower swirl case. A relationship between the injector speed and effective swirl ratio at TDC is strongly supported by the results and maximum spray stagnation onto the piston bowl wall explains the maximum smoke level when rotating co-swirl. Both counter-swirl rotation and increased air-swirl decreases the ignition delay.

A diesel fuel injector has been modified to allow rotation around its axis, driven by an electric motor. The injector was operated up to 6,000 rpm in the current study with a naturally aspirated, optically accessible AVL research engine. The effects of injector rotation on the liquid penetration and dispersion of the spray have been investigated by imaging of Mie-scattered light and flame luminosity. Ambient gas conditions are indirectly controlled by choosing start of injection. Injection timing was set to -45° (premixed-mode), -13° and 4° ATDC. The images show that the spray development is profoundly affected when going from a normal static position of the injector to a rotating movement. Unique liquid cascading phenomena were observed. Injection during the compression stroke into air of low temperature and density shows that the liquid spray tip penetration is unaffected within the field of view (35 mm radius). Enhanced dispersion is obtained however.